Method for cracking hydrocarbons by contact with hot gases



June 28, 1932. I

W. K. LEWIS METHOD FOR CRACKING HYDROCARBONS BY CONTACT WITH HOT GASES 2 Sheets-Sheet Filed May 15, 1928 vam' A53 ORP TION TOWER REA CTIoN CHAMBER.

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atented due 28, 1932 EN K. LEWIS, (DE-NEWTON, SSAGHUSETTS, ASSIGNOR T STANDARD OIL DE- VELOPMENT COMPANY, A CORFQRATION OF DELAWARE METHOD FOR CRACKING l=l RQCARBONS BY CONTACT WITH HOT GASES Application filed may 15, 1928. Serial 1110. 277,821.

The invention relates to improvements in methods and apparatus for cracking hydrocarbons by bringing them into contact with hot non-oxidizing gases. In my United States patent application, Serial No. 59, filed January 2, 1925, a method of this type is utilized for the production of carbon black from hydrocarbon gases. In the present invention the conditions of. operation are modified to secure motor fuel of desirable characteristics and other products from heavier hydrocarbons such as reduced crude, gas oil or the like.

The invention will be fully understood from the following description read in connection with the accompanying drawings in which:

Fig. 1 is a diagrammatic part sectional elevation of one type of equipment suitable for practicing the invention;

Fig. 2 is a similar View showing a modification;

. Fig. 3 is a detail showing an alternative form of reaction chamber.

Referring to Fig. 1, reference numeral 1 denotes a source of hot non-oxidizing gas, such as a gas producer. This may be of usual type containing a deep layer of coke 2 or other combustible material. A pipe 3 opening into the bottom of the producer shaft is connected to a source of 0xygen-conta1ning gas under pressure, for example an air pump-4. Means for preheating the air may be provided but are not generally necessary. A chute 5 serves for the introduction of fuel into the shaft and a pipe'6 for conveying the hot gases therefrom to a reaction chamber 7. Hydrocarbons to be cracked are discharged into chamber 7 through pipe 8.

The reaction product is taken off through pipe 9 to a cooling coil 10 and thence to a separating tank 11. A valved plpe 12 conveys liquid products from the separating tank to a recycle line, storage tank, or other equipment not shown. A line 13 in which a pressure control valve 14 is installed carries the gaseous and vaporous products to a recovery system, which may lnclude an absorption tower 15. A pump 16 1s prov1ded in line 13. An absorption medium is applied to the top of the tower through pipe 17 and the dissolved product is withdrawn via pipe 18 from the bottom. A gas line 19 conveys undlssolved gases from tower for venting through branch 20 or recycling through branch 21. A by-pass 22 connects line 21 with plpe 6. Valves 20a, 21a and 22a are provided in the respective lines for controlling the flow of gas.

Referring now to Fig. 2, the gas producer 1, reaction chamber 7 and absorption tower 15 are arranged and connected substantially.

as above described. In Fig. 2, however, means are provided for'utilizing the heat of the reaction products from chamber 7. For this purpose coils 23 and 24 are arranged in a counter current heat exchanger 25. Hydrocarbons to be cracked enter coil 23 through pipe 26 and the recycled gas from tower 15 enters coil 2& through pipe 27. The preheated hydrocarbons pass through pipe 28 into chamber 7 and the preheated recycled gas is forced into pipe 6 through line 29.

In Fig. 3 T have illustrated a preferred type of reaction chamber designated 7 This chamber is elongated and receives the hot combustion gases through a plurality of nozzles 30 arranged in a vertical series. The nozzles have heat insulating jackets 31. Hydrocarbons to be cracked enter chamber 7 at a point above the nozzles, as by pipe 32.

The following example illustrates the method of operation. Air from pipe 3 is blown through the ignited mass of coke or other combustible material in gas producer '1. The bed of combustible material should be deep so that the gases passing from it are substantially devoid of oxygen. I I prefer to work the producer so as to yield a mixture consisting mainly of carbon monoxide and nitrogen at about 1200 to 1800 C. The producer operates most efficiently under these conditions. The temperature of the gaseous mixture is too high, however, and is therefore reduced and controlled within the desired limits as by diluting with a cooler gas. In one method of operation the temperature of the gaseous mixture is controlled by feeding in cool gas from the recycle line 21 and by-pass 22. 'A further regulation may be obtained by passing gas into the base of the producer through line 21, but this is less satisfactory. Since the hydrocarbon gases in the recycled gas stream are mostly methane and other resistant light hydrocarbons, they are not substantially decomposed by contact with the hot gas, provided they are recycled in proper quantity. e

Under good operating conditions it is necessary to recycle approximately two volumes of stripped gas from tower 15 for each volume of hot combustion gas, both quantities assumed to be measured under the same conditions of temperature and pressure. The rate of recycling may of course be varied in accordance with particular requirements.

It will be determined to a considerable extent by the amount of preheat imparted to the feed oil and the recycled gas in coils 23 and 24 in heat exchanger 25, when the construction shown in Fig. 2 is used. It will be understood that the producer gas may be cooled by other means than that described.

The temperature of the reaction chamber 7 can be controlled in part by regulating the amount of hot producer gas passing to it. This, however, is not so satisfactory as tempering the gases, since the localized contact of the hydrocarbon stock with extremely hot gas before it has been cooled by dilution is likely to crack a part of the stock to an excessive degree. The risk of carrying the cracking reaction too far is obviated to a substantial extent b injecting the hot gas in small increments t rough a series of nozzles as illustrated in Fig. 3. With this arrangement the entering hydrocarbon vapors and/or liquid progressively dilute the hot gases and prevent over cracking.

The temperature in the reaction chamber 7 should be at least 550 C. and temperatures as hi h as 600 C. are sometimes practical if refractory hydrocarbon stocks are being treated. Higher temperatures usuallyresult in too extensive decomposition. The temperature of the hot gases entering the reaction chamber must be at least 650 C. It is preferable to have them at least at 800 C. and with proper precautions it is sometimes possible to admit them at temperatures as high as 1100 C. without encountering bad effects.

The pressure in the reaction chamber may be substantially atmospheric or higher pressure such as 50 to 100 pounds per square inch may be used. When working with stocks of relatively low volatility, such as reduced crude, atmospheric pressure or slight positive pressure is recommended because it permits more rapid vaporization of the stock. Higher pressures on the other hand make it easier to strip heavier hydrocarbons out of the reaction product and permit higher velocities through the system. The operating pressure depends on the relative importance of such factors under the conditions of the individual case. Means for controlling pressure may be supplied at any suitable point. A control valve in the line 13 leading from the separating tank 11 is generally desirable.

The hydrocarbon stock, for example reduced crude, is vaporized or showered into the path of the hot vapors from pipe 6. The stock should be preheated either by the means described or an equivalent such as a separately fired coil. Limited thermal decomposition takes place in the reaction chamber with little or no separation of carbon. The reaction product is cooled in 10. The cool product is discharged into tank 11 from which gases and vapors pass to the recovery system. This is desirably an oil scrubber, for example tower 15, which receives gas oil or other suitable hydrocarbon solvent at the top through line 17 and discharges an absorption stock containing the dissolved reaction product through line 18. The absorption stock is distilled for the recovery of the dissolved components. The liquid product from tank 11 may be recycled or otherwise disposed of. Other recovery means may be provided instead of the absorption system described, for example a cooling and compression system, charcoal absorption or the like.

When heavy charging stocks are used they may advantageously be injected into the reaction chamber 7 by means of a hot gas which may be a portion of the recycled gas.

The present method is designed primarily for the production of motor fuel having good knock rating and high unsaturated content. However, valuable by-pro'ducts maybe obtained. For example, the system may be operated to yield carbureted producer gas by restricting the amount of recycling and allowing a proper quantity of lower boiling hydrocarbons to escape from the recovery system with the vent gas. The liquid reaction product collecting in 11 may be rectified for the separation of kerosene and gas oil fractions, either or both of which may be recycled or otherwise utilized.

In all cases cracking takes place in a zone entirely separate from that in which the combustion gases are produced. Contact masses or other suitable means may be supplied in the reaction chamber 7 if desired for bring= ing the gases and hydrocarbons into intimate contact.

The following description is merely illustrative of preferred forms of the invention and various changes and alternative arrangements may be made within the scope of the appended claims in which it is my intention to claim all novelty inherent in the invention as broadly as the prior art permits.

I claim:

1. Method of cracking hydrocarbons to produce lower boiling products, comprising making producer gas at a temperature between 1200 and 1800 (1., partially cooling resales said gas, injecting the partially cooled gas into a reaction zone to produce a crackln temperature up to approximately 600 therein, introducing hydrocarbons into said reaction zone wherein they are thermally decomposed by the hot gases, withdrawing the reaction product, and recovering lower boiling hydrocarbon components therefrom.

2. Method of cracking hydrocarbons to produce lower boiling products substantially without formation of carbon, comprising passing producer gas at a temperature of between approximately 1200 and 1800 C. from a zone in which said gas is formed, diluting said gas with a cooler non-oxidizing gas, injectin the mixed gases into a reaction zone, intro ucing hydrocarbons into said reaction zone wherein they are thermally decomposed and a temperature not substantially greater than 600 C. is maintained by the hot gases,

withdrawing the reaction product, and recovering lower boiling hydrocarbon components therefrom.

3. Method according to claim 2, in which the reaction product is separated into a liquid fraction and a vaporous fraction, the vaporous fraction is passed through a recovery system in which gasoline constituents are sepa rated, and the residual gases and vapors are discharged for return in part to the system.

a. Method of cracking hydrocarbons to produce lower boiling products comprising operating a gas producer to form a hot gaseous mixture consisting essentially of carbon monoxide and nitrogen, bringing the gaseous mixture into a reaction zone, contacting hydrocarbons therein with said gaseous mixture, at a temperature between about 550 C. and 600 (1, withdrawing the reaction products, separating gasoline constituents and residual gas therefrom, passing a portion of the residual gas in heat exchange relation with'the hot products from the reactiton zone,

and admixing the heated residual gas with the hot gaseous mixture passing from the gas producer to the reaction zone.

WARREN K. LEWIS. 

